Does FROM_UNIXTIME heavily affect the performance of a query like this:
(
(calltasks.task_dueDate = '".$date."') # Tasks of this date
OR
(calltasks.task_dueDate < '".$date."' AND calltasks.task_status = 'scheduled') # Tasks still available on this date
OR
(FROM_UNIXTIME(calltasks.task_executionTime, '%Y-%m-%d') = '".$date."') # Tasks finished this date
)
Or I should be fine with it ??
Rather than converting your UNIX time to a formatted string, then comparing those (as you currently are), you would be better to use UNIX_TIMESTAMP() to convert your $date variable to a UNIX time and then compare integers (checking the difference is no more than 24 hours). Integer comparison will always be faster than string comparison:
(calltasks.task_executionTime - UNIX_TIMESTAMP('$date')) BETWEEN 0 AND 86400
Alternatively, you may find that you already have the UNIX timestamp value of $date somewhere readily available in the language from which you are invoking this query: PHP, for example, stores dates as UNIX timestamps.
Note that you should be absolutely certain that $date cannot be manipulated to contain SQL if you are inserting it into your query in this fashion; if there is any doubt, you should use a prepared statement: if you don't know why, or what they are, read about Bobby Tables.
Related
I'm using the America/New York timezone. In the Fall we "fall back" an hour -- effectively "gaining" one hour at 2am. At the transition point the following happens:
it's 01:59:00 -04:00
then 1 minute later it becomes:
01:00:00 -05:00
So if you simply say "1:30am" it's ambiguous as to whether or not you're referring to the first time 1:30 rolls around or the second. I'm trying to save scheduling data to a MySQL database and can't determine how to save the times properly.
Here's the problem:
"2009-11-01 00:30:00" is stored internally as 2009-11-01 00:30:00 -04:00
"2009-11-01 01:30:00" is stored internally as 2009-11-01 01:30:00 -05:00
This is fine and fairly expected. But how do I save anything to 01:30:00 -04:00? The documentation does not show any support for specifying the offset and, accordingly, when I've tried specifying the offset it's been duly ignored.
The only solutions I've thought of involve setting the server to a timezone that doesn't use daylight savings time and doing the necessary transformations in my scripts (I'm using PHP for this). But that doesn't seem like it should be necessary.
Many thanks for any suggestions.
I've got it figured out for my purposes. I'll summarize what I learned (sorry, these notes are verbose; they're as much for my future referral as anything else).
Contrary to what I said in one of my previous comments, DATETIME and TIMESTAMP fields do behave differently. TIMESTAMP fields (as the docs indicate) take whatever you send them in "YYYY-MM-DD hh:mm:ss" format and convert it from your current timezone to UTC time. The reverse happens transparently whenever you retrieve the data. DATETIME fields do not make this conversion. They take whatever you send them and just store it directly.
Neither the DATETIME nor the TIMESTAMP field types can accurately store data in a timezone that observes DST. If you store "2009-11-01 01:30:00" the fields have no way to distinguish which version of 1:30am you wanted -- the -04:00 or -05:00 version.
Ok, so we must store our data in a non DST timezone (such as UTC). TIMESTAMP fields are unable to handle this data accurately for reasons I'll explain: if your system is set to a DST timezone then what you put into TIMESTAMP may not be what you get back out. Even if you send it data that you've already converted to UTC, it will still assume the data's in your local timezone and do yet another conversion to UTC. This TIMESTAMP-enforced local-to-UTC-back-to-local roundtrip is lossy when your local timezone observes DST (since "2009-11-01 01:30:00" maps to 2 different possible times).
With DATETIME you can store your data in any timezone you want and be confident that you'll get back whatever you send it (you don't get forced into the lossy roundtrip conversions that TIMESTAMP fields foist on you). So the solution is to use a DATETIME field and before saving to the field convert from your system time zone into whatever non-DST zone you want to save it in (I think UTC is probably the best option). This allows you to build the conversion logic into your scripting language so that you can explicitly save the UTC equivalent of "2009-11-01 01:30:00 -04:00" or ""2009-11-01 01:30:00 -05:00".
Another important thing to note is that MySQL's date/time math functions don't work properly around DST boundaries if you store your dates in a DST TZ. So all the more reason to save in UTC.
In a nutshell I now do this:
When retrieving the data from the database:
Explicitly interpret the data from the database as UTC outside of MySQL in order to get an accurate Unix timestamp. I use PHP's strtotime() function or its DateTime class for this. It can not be reliably done inside of MySQL using MySQL's CONVERT_TZ() or UNIX_TIMESTAMP() functions because CONVERT_TZ will only output a 'YYYY-MM-DD hh:mm:ss' value which suffers from ambiguity problems, and UNIX_TIMESTAMP() assumes its input is in the system timezone, not the timezone the data was ACTUALLY stored in (UTC).
When storing the data to the database:
Convert your date to the precise UTC time that you desire outside of MySQL. For example: with PHP's DateTime class you can specify "2009-11-01 1:30:00 EST" distinctly from "2009-11-01 1:30:00 EDT", then convert it to UTC and save the correct UTC time to your DATETIME field.
Phew. Thanks so much for everyone's input and help. Hopefully this saves someone else some headaches down the road.
BTW, I am seeing this on MySQL 5.0.22 and 5.0.27
MySQL's date types are, frankly, broken and cannot store all times correctly unless your system is set to a constant offset timezone, like UTC or GMT-5. (I'm using MySQL 5.0.45)
This is because you can't store any time during the hour before Daylight Saving Time ends. No matter how you input dates, every date function will treat these times as if they are during the hour after the switch.
My system's timezone is America/New_York. Let's try storing 1257051600 (Sun, 01 Nov 2009 06:00:00 +0100).
Here's using the proprietary INTERVAL syntax:
SELECT UNIX_TIMESTAMP('2009-11-01 00:00:00' + INTERVAL 3599 SECOND); # 1257051599
SELECT UNIX_TIMESTAMP('2009-11-01 00:00:00' + INTERVAL 3600 SECOND); # 1257055200
SELECT UNIX_TIMESTAMP('2009-11-01 01:00:00' - INTERVAL 1 SECOND); # 1257051599
SELECT UNIX_TIMESTAMP('2009-11-01 01:00:00' - INTERVAL 0 SECOND); # 1257055200
Even FROM_UNIXTIME() won't return the accurate time.
SELECT UNIX_TIMESTAMP(FROM_UNIXTIME(1257051599)); # 1257051599
SELECT UNIX_TIMESTAMP(FROM_UNIXTIME(1257051600)); # 1257055200
Oddly enough, DATETIME will still store and return (in string form only!) times within the "lost" hour when DST starts (e.g. 2009-03-08 02:59:59). But using these dates in any MySQL function is risky:
SELECT UNIX_TIMESTAMP('2009-03-08 01:59:59'); # 1236495599
SELECT UNIX_TIMESTAMP('2009-03-08 02:00:00'); # 1236495600
# ...
SELECT UNIX_TIMESTAMP('2009-03-08 02:59:59'); # 1236495600
SELECT UNIX_TIMESTAMP('2009-03-08 03:00:00'); # 1236495600
The takeaway: If you need to store and retrieve every time in the year, you have a few undesirable options:
Set system timezone to GMT + some constant offset. E.g. UTC
Store dates as INTs (as Aaron discovered, TIMESTAMP isn't even reliable)
Pretend the DATETIME type has some constant offset timezone. E.g. If you're in America/New_York, convert your date to GMT-5 outside of MySQL, then store as a DATETIME (this turns out to be essential: see Aaron's answer). Then you must take great care using MySQL's date/time functions, because some assume your values are of the system timezone, others (esp. time arithmetic functions) are "timezone agnostic" (they may behave as if the times are UTC).
Aaron and I suspect that auto-generating TIMESTAMP columns are also broken. Both 2009-11-01 01:30 -0400 and 2009-11-01 01:30 -0500 will be stored as the ambiguous 2009-11-01 01:30.
I think micahwittman's link has the best practical solution to these MySQL limitations: Set the session timezone to UTC when you connect:
SET SESSION time_zone = '+0:00'
Then you just send it Unix timestamps and everything should be fine.
But how do I save anything to 01:30:00
-04:00?
You can convert to UTC like:
SELECT CONVERT_TZ('2009-11-29 01:30:00','-04:00','+00:00');
Even better, save the dates as a TIMESTAMP field. That's always stored in UTC, and UTC doesn't know about summer/winter time.
You can convert from UTC to localtime using CONVERT_TZ:
SELECT CONVERT_TZ(UTC_TIMESTAMP(),'+00:00','SYSTEM');
Where '+00:00' is UTC, the from timezone , and 'SYSTEM' is the local timezone of the OS where MySQL runs.
Mysql inherently solves this problem using time_zone_name table from mysql db.
Use CONVERT_TZ while CRUD to update the datetime without worrying about daylight savings time.
SELECT
CONVERT_TZ('2019-04-01 00:00:00','Europe/London','UTC') AS time1,
CONVERT_TZ('2019-03-01 00:00:00','Europe/London','UTC') AS time2;
This thread made me freak since we use TIMESTAMP columns with On UPDATE CURRENT_TIMESTAMP (ie: recordTimestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP) to track changed records and ETL to a datawarehouse.
In case someone wonder, in this case, TIMESTAMP behave correctly and you can differentiate between the two similar dates by converting the TIMESTAMP to unix timestamp:
select TestFact.*, UNIX_TIMESTAMP(recordTimestamp) from TestFact;
id recordTimestamp UNIX_TIMESTAMP(recordTimestamp)
1 2012-11-04 01:00:10.0 1352005210
2 2012-11-04 01:00:10.0 1352008810
I was working on logging counts of visits of pages and displaying the counts in graph (using Flot jQuery plugin). I filled the table with test data and everything looked fine, but I noticed that at the end of the graph the points were one day off according to labels on x-axis. After examination I noticed that the view count for day 2015-10-25 was retrieved twice from the database and passed to Flot, so every day after this date was moved by one day to right.
After looking for a bug in my code for a while I realized that this date is when the DST takes place. Then I came to this SO page...
...but the suggested solutions was an overkill for what I needed or they had other disadvantages. I am not very worried about not being able to distinguish between ambiguous timestamps. I just need to count and display records per days.
First, I retrieve the date range:
SELECT
DATE(MIN(created_timestamp)) AS min_date,
DATE(MAX(created_timestamp)) AS max_date
FROM page_display_log
WHERE item_id = :item_id
Then, in a for loop, starting with min_date, ending with max_date, by step of one day (60*60*24), I'm retrieving the counts:
for( $day = $min_date_timestamp; $day <= $max_date_timestamp; $day += 60 * 60 * 24 ) {
$query = "
SELECT COUNT(*) AS count_per_day
FROM page_display_log
WHERE
item_id = :item_id AND
(
created_timestamp BETWEEN
'" . date( "Y-m-d 00:00:00", $day ) . "' AND
'" . date( "Y-m-d 23:59:59", $day ) . "'
)
";
//execute query and do stuff with the result
}
My final and quick solution to my problem was this:
$min_date_timestamp += 60 * 60 * 2; // To avoid DST problems
for( $day = $min_date_timestamp; $day <= $max_da.....
So I am not staring the loop in the beginning of the day, but two hours later. The day is still the same, and I am still retrieving correct counts, since I explicitly ask the database for records between 00:00:00 and 23:59:59 of the day, regardless of the actual time of the timestamp. And when the time jumps by one hour, I am still in the correct day.
Note: I know this is 5 year old thread, and I know this is not an answer to OPs question, but it might help people like me who encountered this page looking for solution to the problem I described.
I am using UNIX_TIMESTAMP(), but when I pass dates that are far in the future, it starts returning NULL at some point.
For example, the following SQL gives me a proper, non-null result: SELECT UNIX_TIMESTAMP(ADDDATE(NOW(), INTERVAL 18 YEAR)).
However, if I increase that value by one year, the returned value becomes NULL: SELECT UNIX_TIMESTAMP(ADDDATE(NOW(), INTERVAL 19 YEAR))
What is the problem here? Could it be an integer overflow? And how do I solve it?
I am using the following MariaDB version: Ver 15.1 Distrib 10.4.7-MariaDB, for Linux (x86_64) using readline 5.1
Unix time (signed 32-bit) ends on 03:14:07 Tuesday, 19 January 2038 UTC
Related: Year_2038_problem
UNIX_TIMESTAMP:
Timestamps in MariaDB have a maximum value of 2147483647, equivalent to 2038-01-19 05:14:07. This is due to the underlying 32-bit limitation. Using the function on a date beyond this will result in NULL being returned. Use DATETIME as a storage type if you require dates beyond this.
SELECT ADDDATE(NOW(), INTERVAL 19 YEAR) -- DATETIME
-- 2038-09-07 18:42:39
As stated in my above comment I couldn't make it work passed the 2038 Epochalipse date limit, not even converting the field to DATETIME. There are probably other considerations affecting this eventual solution.
The only workaround that I could find was to get the date out of the DB from PHP and use the strtotime() PHP function to get the UNIX TIMESTAMP from it.
SELECT DATE_FORMAT(CONVERT(thedatefield, DATETIME),"%Y-%m-%dT%TZ") AS thedatefield
As there exist different date formats (American, English, Latin, etc...) which are incompatible and a possible source of trouble, I am using two MySQL/ MariaDB functions to flatten the output to an ISO date (YYY-MM-DDThh:mm:ss). Once the output is uniform in any system you can pass the output to the strtotime() PHP function with the confidence that it will be correctly parsed to a UNIX TIMESTAMP.
CONVERT: casts the date to a datetime DB type.
DATE_FORMAT: converts the date to ISO format (YYY-MM-DDThh:mm:ss).
You can of course remove those functions and adapt the solution to the particularities of your system to reduce the processing load. This proposed solution will work with any system date style.
In case of just one register being returned by PHP (the simplest case) I set the first dimension of the returned 2D or table array to 0
date("U",strtotime($php_array[0][thedatefield]))
The PHP date() function by virtue of the "U" flag will convert the DB output to a UNIX TIMESTAMP without the 32 bit 2038 Epochalipse limitation.
I have a table with a varchar column DateFrom that has this format:
2014-02-22T08:08:00
I want an sql that prints 08:08 and one that prints 22-02-2014 but i can't seem to get the time function to work.
What i'm trying to do is get all entries in DateFrom and print them as just time (HH:MM)
and the same with date.
Altough I think string functions are a better option in this case (like #hakre answered) and less cpu expensive, you can also achieve this goal using the STR_TO_DATE, DATE and TIME function.
SELECT
DATE(STR_TO_DATE('2014-02-22T08:08:00', '%Y-%m-%dT%H:%i:%s')),
TIME(STR_TO_DATE('2014-02-22T08:08:00', '%Y-%m-%dT%H:%i:%s'))
If you're not looking for date/time but for string functions, they are available here:
http://dev.mysql.com/doc/refman/5.0/en/string-functions.html
One string function that I think is useful for your substring operation is SUBSTRING. You can tell per the varchar column that you want a sub-string starting from a position for a certain length with it:
SUBSTRING(DateFrom FROM 1 FOR 8) AS DateName -- "2014-02-22"
SUBSTRING(DateFrom FROM 10 FOR 5) AS TimeName -- "08:08"
Use other string functions to concatenate parts in the order you need it.
Alternatively you can cast your varchar string in that format to a datetime type and then format as needed:
CAST(DateFrom AS datetime)
See the Mysql manual for more information about casting types and the date-time functions that are available:
http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html
SQL Example:
SET #DateFrom = '2014-02-22T08:08:00';
SELECT DATE(CAST(#DateFrom AS datetime)); -- '2014-02-22'
SELECT TIME(CAST(#DateFrom AS datetime)); -- '08:08:00'
I want to record the start and end times of, say, movies playing at the cinemas. I need to store the date (e.g. Jan 1, 2011), start time (e.g. 9:00am), and end time (e.g. 11am). Should I used DateTime? I've seen some implementations wherein an INT is used to represent time in minutes (e.g. 0 = 12 midnight, 1 = 12:01am, etc.). I'm not sure if there is some sort of benefit to using INT over DateTime.
Suggestions?
EDIT 1:
Expanding on the idea of using INT as described above, the table would probably have the following columns:
date (e.g. Jan 1, 2011)
start_time (e.g. 540 - to indicate 9am)
end_time (e.g. 660 - to indicate 11am)
In my opinion a person should use the datatype that better fits and describes the reality. In this case I would like to use Datetime.
For me better is to use to DateTime columns, because INT have hidden interpretation. Without documentation you don't know what is it really: second, minutes, months, ...
It is only design approach.
When using DATETIME for start and end fields take into consideration that you may have trouble when "calculationg how long process take", because you should also think about timezones, daylight saving, etc.
Use DATETIME or INT
I prefer to store date&time in unix timestamp (INT), because i can use it in PHP functions like date
echo "Movie will start at ".date("H:i", $row['start_time']);
And it's easy to manipulate with it:
echo "Movie will start in ".(time() - $row['start_time'])." seconds";
Current date and time: http://www.unixtimestamp.com/
If you want to copy movies to next day:
$sql = "SELECT * FROM movies WHERE start_time >= ".strtotime("today 00:00")." AND start_time <= ".strtotime("today 23:59");
// query..
foreach($results as $row) {
$new_start = strtotime("+1 day", $row['start_time'];
// insert
}
I would use 'timestamp' for both columns.
Datetime uses 4 bytes whereas Timestamp uses 8 bytes therefore more efficient.
Comparisons of timestamps is significantly faster than of datetimes.
When it comes to time zones leap years and daylight saving you may run into trouble with the int technique as you will have to take those changes into account manually. Maybe this won't be an issue for you.
I'd say you have two appropriate formats:
"start time - duration" (datetime, int) or (timestamp, int)
"start time - end time" (datetime, datetime) or (timestamp, timestamp)
One of the big problems with date-time stuff is the DST jumps twice a year, throwing off your calculations by an hour. Traveling between timezones is equally confusing. If you use the time/time notation, your duration may vary. If you use the time/duration notation, your end time may vary. Whichever one of these two representations is the most appropriate therefore depends on your usage (you may need to use a hybrid approach).
For movie show times, I'd say storing a start time and a duration in minutes is the more appropriate format. The run-time of the movie is a given, the end time comes after the fact.
I have a column that uses time stamp. My question is I am a bit confused about how to make queries against it,how would I say
Where $time is after X date
Are queries made in local time or CUT?
When I just try to do where andthe post date /time I get an error because of the space and if I quote it I think it takes it as a string : /
What format do I use for the date in the WHERE clauss !?!?
You can use the normal logical comparisons, for example:
SELECT * FROM table WHERE date >= '2010-01-31'
SELECT * FROM table WHERE date >= '2010-01-31 12:01:01'
Time is generally in your current local time, but you can run the query "SELECT CURTIME()" to check. Also, make sure you have the year-month-date in the right order... that can cause issues.
The manual has more details:
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html
Assuming you talk about TIMESTAMP column type (not Unix timestamp) the format is either 'YYYY-MM-DD HH:MM:SS' (quoted) or YYYYMMDDHHMMSS
Atually, in the first case you can use any spearators you wish (or none), only numbers are taken into ccount